1. Field of the Invention
This invention relates to a food sterilizing apparatus and, more particularly, it relates to a food sterilizing apparatus adapted to successively feeding food to a food sterilizing chamber for heating and sterilizing the food under pressure higher than the atmospheric pressure.
2. Prior Art
A variety of sterilizing apparatuses are already known for successively feeding food to a food sterilizing chamber for heating and sterilizing the food, including those disclosed in Japanese Patent Laid-Open Publication Nos. 49-71177, 51-42391 and 64-51069.
With any of these sterilizing apparatuses, a conveyor means for advancing the food has to be arranged within the food sterilizing chamber of the apparatus. A conveyor means arranged within a sealed chamber can make the entire configuration of the apparatus rather complicated and is disadvantageous to maintain the chamber in an aseptic condition.
In an attempt to solve the above identified technological problem of the known art, different sterilizing apparatuses have been proposed to successively advance the food in a sealed and heated sterilizing chamber without a conveyor means arranged within the chamber. For example, U.S. patent application Ser. No. 08/395,111 filed on Feb. 27, 1995 and assigned to the assignee of the present application, suggested a food sterilizing apparatus comprising a heater for sterilizing food fed successively thereto at high temperature and under high pressure. The disclosed apparatus additionally comprises a pressure regulating chamber arranged between a food feeding section held in communication with the atmosphere and the heated and pressurized heating vessel (heater). First and second sealing gates are disposed, respectively, between the food feeding section and the pressure regulating chamber and between the pressure regulating chamber and the heating vessel. For advancing food from the food feeding section to the heating vessel, at first, the first sealing gate is opened to make the food feeding section communicate with the pressure regulating chamber and food is brought into the pressure regulating chamber while the second sealing gate is closed and the pressure regulating chamber does not communicate with the heating vessel. Secondly, the first sealing gate is closed to sealedly isolate the pressure regulating chamber and raise the inner pressure (or both the inner pressure and the temperature) of the pressure regulating chamber to the level of the inner pressure (or both the inner pressure and the temperature) of the heating vessel. Then, the second sealing gate is opened to make the pressure regulating chamber communicate with the heating vessel, keeping the first sealing gate under a closed condition, and foods are fed into the hot and pressurized heating vessel for sterilization.
With the above arrangement, the time required for the inner pressure (or both the inner pressure and the temperature) of the pressure regulating chamber to be raised to the level of the inner pressure (or both the inner pressure and the temperature) of the heating vessel for each operation (hereinafter referred to stand-by time) is useless and wasteful in terms of the productivity of the apparatus because it is not used for feeding foods from the food feeding section into the heating vessel. The inner pressure (or both the inner pressure and the temperature) of the pressure regulating chamber is regulated by introducing the steam through a pipe connected to a steam source such as a boiler. On the pipe, there is provided a pressure-reducing valve and a control valve. The steam to be fed into the pressure regulating chamber from the vapor source under pressure is reduced to a predetermined level by a pressure-reducing valve and fed into the pressure regulating chamber when the control valve is opened.
With such an arrangement, however, the steam source is inevitably separated away from the pressure regulating chamber and hence it takes considerable time for the inner pressure of the pressure regulating chamber to be raised to the level of the inner pressure of the heating vessel. This stand-by time provides a major drawback in the operation of the food sterilizing apparatus from the viewpoint of efficiency and productivity.
Additionally, after feeding a given number of foods into the heating vessel, the second sealing gate is closed to sealedly close the pressure regulating chamber and then the inner pressure of the pressure regulating chamber is reduced to level of atmospheric pressure by means of a pressure reducing means such as a valve. Then, the first sealing gate is opened to receive the food from the food feeding section within the pressure regulating chamber.
Since the food feeding section is in communication with the atmosphere and the pressure regulating chamber is also held to the atmospheric pressure, ambient air can easily flow into the pressure regulating chamber once the first sealing gate separating the food feeding section and the pressure regulating chamber is opened. As a result, the temperature of the pressure regulating chamber can be lowered by ambient air flowing into the chamber to further increase the stand-by time required to raise the pressure and the temperature of the pressure regulating chamber to the respective levels of those of the heating vessel and reduce the efficiency of the operation of the apparatus.
Further, the ambient air flowed into the pressure regulating chamber is flowed into the heating vessel and obstructs the contact of the vapor to the food and lowers the efficiency of the sterilization.